In the last two decades, the automatic mechanisation of the extraction of flatly disposed coal seams, of 0 to 20 gon (0 to 18 degrees), and of slightly inclined deposits, of gradients of 20 to 40 gon (18 to 36 degrees), has resulted in output rates of up to 1,500 t/h with the use of mining ploughs in plough appliances, and over 2,600 t/h with the use of shearer loaders. Meanwhile, more than 90% of the quantity of coal excavated underground originates from flat or slightly inclined deposits, since the latter can be excavated substantially more economically by means of the existing mining technology than can coal seams or other mineral deposits in a greatly inclined disposition, of a gradient of more than 40 gon (36 degrees), or in a steep disposition, of 60 to 100 gon (54 to 90 degrees).
A coal plough, which is provided with a bit carrier that is pivotable according to the direction of travel, and which is moved back and forth reversingly in the underground face, parallelwise in relation to the excavation front, by means of a continuous plough chain, has proved successful for the excavation of flatly disposed coal seams. Each bit carrier is provided with a multiplicity of bit pockets, in which, in turn, plough bits can be accommodated in a demountable manner. In order to achieve a different excavation height by means of the same coal plough, there is additionally provided a roof bit carrier, which is arranged centrally between the two pivotable bit carriers and which can be extended or retracted in an appropriate manner, for example by means of a worm gearing. Insofar as possible, the same bit pocket is fixed both on the pivotable bit carriers and on the roof bit carrier, in order to minimize the production costs. DE 39 23 969 C2 describes, by way of example, such a coal plough having pivotable bit carriers and roof bit carriers.
There are multiple differing possibilities for anchoring a plough bit in a bit pocket in such a way that the necessary mining work, in particular the excavation of coal or other minerals at the excavation front, can be performed reliably and with an adequate tool life by means of the plough bits. DE 101 61 015 A1 describes, merely by way of example, a bit arrangement having bit pockets and a plough bit that can be fastened in the bit pocket.